The fluorescence lidars which are in existence at the present time detect the fluorescence radiation in certain spectral bands, which are selected by means of interference filters or of a grating spectrometer, and subsequently analyze the data extracted for the purpose of undertaking the individual identification of the target and/or of its characteristic features. The lidars of known type exhibit certain disadvantages, which are due, in particular, to the fact that the detected signals are proportional to the intensity of the radiation reflected back in correspondence with certain specific wavelengths. The signals are always influenced by spurious factors such as absorption by the atmosphere, the surface roughness of the target, the losses due to the detection system, which modify the intensity thereof and which thus make a direct detection impossible. In the systems which are in current use, it is therefore necessary to make use of a reference signal, for example an emission line of known intensity, to correct the detected signals and to permit the subsequent processing.